As used in the present application, the term “terahertz” is understood to cover electromagnetic transmission with wavelengths of approximately 3000 um to 10 um corresponding to the range of frequencies from approximately 0.1 THz to approximately 30.0 THz.
Coupling millimeter wave, sub-THZ and THz signals from an integrated circuit to an antenna or interconnect can be problematic in prior known solutions due to three key issues.
The first issue involves the losses that occur in back-end materials due to skin depth in metals, and dielectric losses in oxides and nitrides. To achieve high gain antennas, or to form high frequency inter-chip interconnects, large structures are required in the back end processing with respect to wavelength, which greatly increases conductor and dielectric loss.
The second issue involves surface waves, which are propagating modes which appear when a dielectric on a metal interface is large with respect to the signal wavelength. The surface waves cause signal loss (efficiency loss) in antennas and interconnects. FIGS. 1A and 1B depict a graph of the efficiency (shown on the vertical axis of FIG. 1A) where H is the thickness of the dielectric over the top of a metal M1, and the ratio H/lambda_o is shown on the horizontal axis. A typical back end dielectric is 6 microns thick, which is 0.02 (H/lambda_o) at a 1 THz frequency, as shown in FIG. 1A this leads to 10% power loss due to surface waves in patch antennas (similar in a transmission line in the back end). FIG. 1B illustrates the surface wave effects in an example structure showing the energy being transferred as waves along the surface of the dielectric layer, and thus not being efficiently transmitted away from the structure.
The third issue involves the top level metal structures and dielectric materials typically in use for conventional semiconductor devices. These materials, when used for radiators or coupling structures, are too lossy for the efficient radiation and reception of THz frequency signals.
In one prior known approach to address at some of the known problems disclosed in U.S. Pat. No. 8,450,687 (the “'687 patent”), an antenna is integrated directly on the integrated circuit (IC). In the '687 patent, an antenna is formed on the IC with the intent of radiating the energy on the circuit side or top-side of the IC, sometimes referred to as the “front” side. The antenna structure described in the '687 patent is formed in a manner that lowers production costs over prior approaches, in that the antenna build can be incorporated into the IC building process, thus saving additional costs of micromachining as in prior approaches. Another feature of the approach of the '687 patent is that the antenna used improves the radiating efficiency over the prior known planar styled integrated antennas. However, additional problems remain.
FIGS. 2A and 2B illustrate a prior known approach top-side antenna built within an IC fabrication system. In FIG. 2A, a cross sectional view 200 depicts a semiconductor substrate 210a, the doped surface region forming an active area 212, and the metal conductor stack 214. Within the metal conductor stack, a ground plane 220a and an antenna 222a are formed with the antenna 222a at the uppermost portion of the metal conductor stack 214. The metal conductor stack 214 can be formed from a multiple level metal structure with conductors formed at levels separated by dielectric layers such as are formed over the surface of semiconductor substrates in integrated circuit fabrication. In FIG. 2B, a top view 202 of this structure is illustrated again showing the semiconductor substrate 210b, the ground plane 220b and the antenna structure 222b. Additionally, a number of bond pads 224 and bond wires 230 are shown to help illustrate that this antenna structure is formed on the top or circuit side of a semiconductor substrate such as a silicon, silicon germanium, gallium arsenide or other semiconductor wafer. With the antenna 222a formed on the top-side of the semiconductor substrate, the energy radiates upwards away from the top side of the wafer or substrate 210b. 
FIG. 3 depicts in 300 a prior known approach a top-side antenna such as is depicted in FIGS. 2A and 2B in operation radiating signals, and a corresponding balloon graph 340. Illustrated in FIG. 3 is an arrangement 300 including a wafer or semiconductor substrate 310, a top-side antenna 322, a plurality of bond pads 324, and a plurality of bond wires 330. The balloon graph 340 represents the simulated energy radiated by the top-side antenna 322 in operation. In this arrangement 300, the peak gain was found in simulations to be approximately 7 dB as indicated by the graph scale 342 in FIG. 3 and the balloon graph 340.
Continuing improvements are therefore needed for methods and for couplers or antennas that are compatible with commercial semiconductor processes and that can efficiently transmit and receive signals at THz and sub-THz frequencies. A higher gain antenna is desirable as well as the ability to more efficiently couple the radiated energy to other THz components.